按兩位列分組

Question

我想GROUP BY兩位列的值爲true。但我有兩列分開，我怎麼能加入他們的位列是真實的？輸出

SELECT  employees.employee_id, employees.last_name, 
      employees.first_name, employees.middle_name, 
      employee_role.isAdmin, employee_role.isEmployee 
FROM  employees 
INNER JOIN employee_role ON employee_role.employee_id = employees.id 
INNER JOIN passwords ON passwords.id = employees.password_id 
WHERE  employees.employee_id = pIN_employeeId AND passwords.password = pIN_password; 

草案：

employee_id | last_name | first_name | middle_name | isAdmin | isEmployee 
------------+-----------+------------+-------------+---------+------------ 
    20140540 | Armstrong | Billie Joe |  A  | 0  | 1 
    20140540 | Armstrong | Billie Joe |  A  | 1  | 0 

預期輸出：

employee_id | last_name | first_name | middle_name | isAdmin | isEmployee 
------------+-----------+------------+-------------+---------+------------ 
    20140540 | Armstrong | Billie Joe |  A  | 1  | 1 

Answer 1

你可以使用Max與GROUP BY：

SELECT  employees.employee_id, employees.last_name, 
      employees.first_name, employees.middle_name, 
      Max(employee_role.isAdmin), 
      Max(employee_role.isEmployee) 
FROM  employees 
INNER JOIN employee_role ON employee_role.employee_id = employees.id 
INNER JOIN passwords  ON passwords.id = employees.password_id 
WHERE  employees.employee_id = pIN_employeeId AND passwords.password = pIN_password 
GROUP BY employees.employee_id; 

如果EMPL oyee_id不是主鍵，你將需要添加其他列的GROUP BY子句中還有：

GROUP BY employees.employee_id, employees.last_name, 
      employees.first_name, employees.middle_name; 

在其他數據庫甚至需要添加這些列。

如果你只希望包括具有與isAdmin位集的記錄，並且還具有與isEmployee集的記錄，排除所有其他情況下的員工，然後添加HAVING條款是這樣的：

SELECT  employees.employee_id, employees.last_name, 
      employees.first_name, employees.middle_name, 
      Max(employee_role.isAdmin), 
      Max(employee_role.isEmployee) 
FROM  employees 
INNER JOIN employee_role ON employee_role.employee_id = employees.id 
INNER JOIN passwords  ON passwords.id = employees.password_id 
WHERE  employees.employee_id = pIN_employeeId AND passwords.password = pIN_password 
GROUP BY employees.employee_id 
HAVING  Max(employee_role.isAdmin) = 1 
AND  Max(employee_role.isEmployee) = 1;